PROCESS FOR PRODUCING A HIGH MOLECULAR WEIGHT EPOXY RESIN

Abstract: The present invention provides a process for producing a high molecular weight epoxy resin by polymerizing an epoxy resin having an average epoxide group number of two per molecule with a divalent phenol compound in the presence of a glycol ether having no hydroxyl group in alpha -position as a solvent. The preferable glycol ethers used in the present invention include propyleneglycol ethers such as propyleneglycol methylether, propyleneglycolmethylether acetate, propylenepglycol propylether and propyleneglycol monobutylether.

Description: PROCESS FOR PRODUCING A HIGH MOLECULAR WEIGHT EPOXY RESIN The present invention relates to a process for producing a high molecuiar weignt epoxy resin useful for adhesives, insulating mater'als, paints and other coatings, moldings < nd the like, and more particularly relates to a process for producing a high molecular weight epoxy resin in shorter time. A high molecular weight epoxy resin is produced by reacting a bι unctional epoxy resin having relatively low molecular weight with a divalent phenol compound This process is generally called an "advancement" process Regarding the advancement process, for example, Japanese patent publication Kokoku 28-4494 discloses a process using no solvent for polymerization. However, the advanced resm made by that process has an average molecular weight of only about 1 1 ,000. Other advancement processes, which use a solvent for polymerization, are described in Japanese Kokai 04-12124, 54-52200, 60-1 18757, 60-144323 and 60- " 14324. In these publications, the preferred solvents include methylethyl ketone. methyiisobutyl ketone, cyclohexane, ethyleneglycol monoethylether, ethyleneglycol monomethyleth . r and N, N- dimethyl acetamide. However, when the high molecular weight epoxy resin is produced by using a low boiling point solvent such as methylethyl ketone, the reaction time becomes quite ong and a great amount of a catalyst is required, because a reaction temperature cannot be -aised When a high boiling point solvent such as ethyleneglycol ethylether, ethyleneglycol bu ty'et he*- or N, N-dimethyl acetamide is used, the polymerization can be carried out at a high temperature so that polymerization time can be shortened somewhat. However, in terms of product, vity, 't would be desirable to complete the higher molecular weight polymerization m an even shorter time - The purpose of the present invention is to provide a process to produce a higher molecular weight epoxy resin in shorter time by using a solvent having higher non-toxicity. As the result of research and development to solve the above-mentioned problems, the inventor discovered that glycol ethers which contain a primary hydroxyl group with respect to ether groups or other hydroxyl groups may react with an epoxide group in an epoxy resin. That reaction terminates the epoxy resin chain and prevents high mo>ecular weight polymerization. Accordingly, the present invention provides a process for producing a high molecular weight epoxy resin by reacting: (1) an epoxy resin which contains on average more than 1 and less than 3 epoxide groups per molecule with (2) a divalent phenolic compound which contains on average more than 1 and less than 3 phenolic hydroxyl groups per molecule characterized in that the reaction takes place in the presence of a giycolether solvent havng no primary hydroxyl groups The present invention is particularly described below The epoxy resin (hereinafter bifunctional epoxy resin) to be used in the present invention includes any compound substantially having an average of more than 1 and less than 3 epoxide groups per molecule The average number of epoxide groups per molecule is preferably more than 1 8 and less than 3, more preferably less than 2 1 , and most preferably about 2 The bifunctional epoxy resins include, for example, bisphenol A type epoxy res ns, bisphenol F type epoxy resins, bisphenol AD type epoxy resins, bisphenol S type epoxy resins, alicyclic epoxy resins, aliphatic linear type epoxy resins, diglycidyl ethers of divalent phenols diglycidyl ethers of divalent alcohols, halides thereof, hydrogenated thereof and the like Said epoxy resins may be used individually, or as any combination thereof Among said epoxy resins, the preferable epoxy resins include bisphenol A type epoxy resins and bisphenol F type epoxy resins Additionally, the reaction mixture may further contain an additional epoxy component other than the bifunctional epoxy resin, such as a minor amount of epoxy novolac resin, as long as a resultant product has desired properties An epoxy resin as a raw material of the present invention is, without intending to be limited, usually a relatively low molecular weight epoxy resin The bifunctional epoxy resin preferably has an epoxy equivalent weight of 170-400 and more preferably 175-250 It preferably has a number average molecular weight of 340-1000 and more preferably 350-500 In the present invention, for example, D.E R τ " 331 L, D E R • " 383J, D E R ™ 661 (Trademarks of The Dow Chemical Company) may be used as commercialized epoxy resins The divalent phenols in the present invention are used as a chain extender for the polymerization of the epoxy resin, and may be any of phenol compounds having on average more than 1 and less than 3 phenolic hydroxyl groups, preferably having on average 1 8 to 2 1 phenolic hydroxyl groups, most preferably substantially about two phenolic hydroxyl groups The divalent phenols include, for example, monocyclic divalent phenols such as hydroquinone, resorcinol and catechol, polycyclic divalent phenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, halogenated versions thereof, alkyl substituted versions thereof and the like The above-mentioned compounds are used individually, or as any combination thereof Among the above-mentioned divalent phenols, the preferable phenols used the present invention are bisphenol A, and bisphenol F Additionally, the reaction mixture may further contain a phenol component other than the divalent phenols, such as a novolac res or a tnphenol res , as long as a resultant product has desired properties The equivalent ratio of epoxide group : phenolic hydroxyl group is usually 0 7 to 1 4.1 and preferably 0 9 to 1 1 * 1 If the equivalent ratio is less than 0 7, or more than 1 4, the imbalance in stoi chio metry may reduce the molecular weight achieved during advancement In the present invention, the solvent contains glycolethers having no primary hydroxyl groups, i.e. hydroxyl groups bonded to a primary carbon atom. The glycolethers include propyleneglycol ethers having a hydroxyl in β-position. The propyleneglycol ethers in the present invention are able to dissolve raw materials such as the epoxy resins and the phenols, and include, for example, propyleneglycol methylether, propyleneglycolmethylether acetate, propyleneglycol propylether, propyleneglycol monobutylether and the like The preferable propyleneglycol ether is propyleneglycol monobutylether The glycol ether solvent preferably has a boiling point higher than 140°C and more preferably higher than 165°C The maximum boiling point is not critical, but it is preferably no higher than 300°C For the purpose of dissolving the advanced resin, another solvent, for example, such as ketone solvents, amide solvents, ether v ents or aromatic solvents may be added after the ad ancement is completed. The solvent content is preferably 10% to 50% of the reaction mixture, and, more preferably 20% to 40% of the reaction mixture. If the solvent content is less than 10%, the viscosity of the resm may quickly build to high for effective agitation. On the other hand, if the solvent content is more than 50%, the reaction rate may be too slow The polymerization of the present invention is preferably carried out using a catalyst. The catalysts include, for example, imidazoles such as 2-methyl imidazole, tertiary amines such as triethyl amine, tripropyl amine and tributyl amine, phosphonium salts such as ethyltriphenylphosphonium chloride, ethyltriphenyiphosphonium bromide and ethyltriphenylphosphonium acetate, ammonium salts such as benzyltrimethylammonium chloride and benzyltrimethylammonium hydroxide. Suitable catalysts for the present invention are highly active catalysts capable to be used in higher temperature, preferably phosphorous catalysts, especially phosphonium salts such as ethyltriphenylphosphonium acetate. The catalyst concentration is preferably 0.001 to 10 percent by weight, and more preferably 0.01 to 5 percent by weight, based on the reactant solids. If the advanced epoxy resin is intended for food can coating applications, the concentration of the catalyst is most preferably less than 0.25 percents by weight. In the present invention, the polymerization reaction is carried out at a rather high temperature which is lower than both of the boiling point of the polymerization solvent and the decomposition temperature of the polymerization catalyst. The temperature of the advancement reaction is preferably 100 to 250°C and more preferably at ■ 20 to 200°C. The reaction time is preferably 1 to 12 hours and more preferably 3 to 7 hours The polymerization reaction may be carried out by a continuous process or a batch process, under atmospheric pressure, higher pressure or reduced pressure. The advanced epoxy resin made by the process of the present invention preferably has a weight average molecular weight of 20,000 to 200,000, and more preferably 50,000 to 150,000 The molecular we>ght distribution (Mw/Mn) of the advanced resin is preferably 2 to 15 and more preferably 4 to 1 1 Furthermore, the process of the present invention can be used, under preferred conditions and using preferred reagents, to produce an epoxy resin having more than 50,000 (and preferably more than 70,000) weight average molecular weight in 3 to 7 hours. The high molecular weight epoxy resin produced by the process of the present invention may be used as adhesives, insulating materials, moldings solution and powder coatings and the like, and preferably used as paints, more preferably used as paints for metal can coating. EXAMPLES The present invention is particularly illustrated by the following examples In the examples, "parts" means "parts by weight". Examples 1-2 and Comparative Examples A-D: A series of reaction mixtures were made which contained the following components. (1) a liquid epoxy resin with an epoxy equivalent weight of about 180, in the quantities shown in Table 1 ; (2) bisphenol A in the quantities shown in Table 1 ; (3) about 0J8 % (based on solid resin) of ethyltriphenylphosphonium phosphate as catalyst; and (4) the solvent and quantity of solvent shown in Table 1 Each mixture was reacted for 4 or 7 hours at a bout 170°C. A sample of the resulting advanced resin was recovered, and its weight average molecular weight was measured by gel permeation chromatography using polystyrene standards The results are shown in Table 1 The Comparative Examples are not examples of the present invention TABLE 1 Example/ Example 1 Comparative Comparative Comparative Example 2 Comparative Comparative Example A Example B Example C Example D Example LER (Parts) 431 431 431 433 433 309 BIS-A (Parts) 269 269 269 267 267 191 PnB(Parts) 300 300 EB(Parts) 300 DE(Parts) 300 DMAC(Parts) 300 500 ETPPA(%) 0 18 0J 8 0J 8 0 18 ETPPP(%) 0.18 0 18 Reaction Temperature 170 170 170 150 170 150 (°C) Molecular Weight (4hours) 129,000 56,000 56,000 45,000 50,000 17,000 Molecular Weight (7hours) 67,000 72,000 21,000 Abbreviation in Table 1 shows the following compound respectively LER Bisphenol A type epoxy resin BIS-A Bisphenol A PnB Propyleneglycol monobutylether ETPPA Ethyltriphenylphosphonium acetate ETPPP Ethyltriphenylphosphonium phosphate EVALUATION RESULT Comparing Example 1 with Comparative Example A-C, the high molecular weight o polymerization to 29,000 of a weight average molecular weight was available by 4-hour polymerization according to the process of the present invention However, in the polymerization carried out at substantially the same conditions except the solvent used in Comparative Example A-C, the high molecular weight polymerization only to 45,000-56,000 of a weight average molecular weight was available Therefore, it was found that the present 5 invention remarkably enables to a high molecular weight polymerization at the same condition as known process Comparing the result of Example 2 with Comparative Example D, Example 2 achieved an about 3-tιme high molecular weight polymerization in weight average molecular weight, comparing to Comparative Example D, at substantially the same conditions even 0 though the reaction activity was decreased because of the use of ethyltriphenylphosphonium phosphate as polymerization catalyst Therefore, it was found that the present invention remarkably enables to a high molecular weight polymerization in the same conditions as known process As described above, according to the process of the present invention, a higher 5 molecular weight epoxy resin can be produced in shorter time comparing to a prior process using the currently used polymerization solvent 0 5

Claims: WHAT IS CLAIMED IS: 1. A process for producing a high molecular weight epoxy resin by reacting. (1 ) an epoxy resin which contains on average more than 1 and less than 3 epoxide groups per molecule with (2) a divalent phenolic compound which contains on average more than 1 and less than 3 phenolic hydroxyl groups per molecule characterized in that the reaction takes place in the presence of a glycolether solvent having no primary hydroxyl group. 2. The process according to Claim 1 wherein the glycolether is a propyleneglycol ether. 3. The process according to Claim 2 wherein the glycolether is a propyleneglycol monobutylether. 4. The process according to any of Claim 1 to 3 wherein the reaction is carried out in the presence of a catalyst. 5. The process according to any of Claim 1 to 3 wherein the reaction is carried out in the presence of a phosphorous compound as a catalyst. 6. The process according to any of Claim 1 to 3 wherein the reaction is carried out at a temperature of 120-200 °C. 7. The process according to any of Claim 1 to 3 wherein the reaction is carried out at a temperature of 120-200 °C in the presence of a catalyst. 8. The process according to any of Claim 1 to 3 wherein the reaction is carried out at a temperature of 120-200 °C in the presence of a phosphorous compound as a catalyst. 9. A high molecular weight epoxy resin produced by the process according to Claim 1.

Inventors: OGIWARA TOSHIAKI, OGIWARA, TOSHIAKI
Applicants: DOW CHEMICAL CO, OGIWARA TOSHIAKI, OGIWARA, TOSHIAKI, THE DOW CHEMICAL COMPANY
Application year: 1994
Main classification: C08G59
IPC codes: C08G59